The natural articulating joint (diarthrodal joint) comprises adjacent bones having opposing hyaline cartilage surfaces held together by a fibrous collagenous capsule defining a joint space. The inner wall of this capsule is lined with synovial cells. Contained within the capsular joint space is an acellular synovial fluid. The function of the synovial fluid is to provide lubrication for the articulating surfaces.
In a healthy joint, cells within the articular cartilage produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the cartilage with its lubricating qualities. These cells may also secrete small amounts of cytokines as well as matrix metalloproteinases (“MMPs”). These cytokines and MMPs help regulate the metabolism of the hyaline cartilage cells.
There appear to be many causes of degenerative joint disease (DJD). For example, gradual degeneration of the joint may be caused by wear, by trauma, by misalignment, by genetics, or by mechanical instabilities in other portions of the body. In many instances, gradual wear of the hyaline cartilage cause the cells therein (or invading macrophages) to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DJD, genetic factors, such as programmed cell death, or apoptosis can also cause the cells within the hyaline cartilage to emit abnormally large amounts of these cytokines into the extracellular matrix of the hyaline cartilage and synovial fluid.
Although the progression of DJD (also called “osteoarthritis”, or “OA”) is largely dependent upon etiology, it is often the case that the high levels of the cytokines present in the hyaline cartilage begin to mediate the degradation of the extracellular matrix of the cartilage. Concurrently, enzymes in the synovial fluid both upregulate MMPs and downregulate MMP inhibitors. The MMPs (under mediation by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing their water-retaining and lubricious qualities. This degradation leads to a less lubricious hyaline cartilage, thereby increasing the wear upon the hyaline cartilage. This degenerative cascade also often leads to inflammation of the synovial lining, which often produces a thickening and fibrillation of the synovium, and the creation of finger-like villae with the synovium. When the natural regeneration of these cartilage layers is slower than this degenerative process, these changes cause even more mechanical instability, thereby causing the hyaline cartilage cells, the synovium cells and the invading macrophages to emit even more cytokines, thereby typically upregulating MMPs. In sum, osteoarthritis is a degenerative disease that degrades cartilage, which results in pain, restriction of motion and deformity.
In addition to the foregoing, posterior elements of the spine called the “facet joints” help to support axial, torsional and shear loads that act on the spinal column. Furthermore, the facet joints are diarthroidal joints that provide both sliding articulation and load transmission features. The facet's articular surfaces contact in extension, limiting rotation and increasing compressive load. The articular surfaces also contact on one side of the spine in lateral bending and axial rotation, also limiting rotation and transferring load. Early facet osteoarthrosis is relatively mild and is confined to the articular cartilage, capsule, and synovium, but eventually involves the subchondral bone and the margins equally on both sides of a motion segment. With advancing degeneration, the joint capsule undergoes significant changes including increasing fibrosis and vascularization, which has been reported to become hyperemic with infiltration of inflammatory cells, enlargement, and fibrosis.
The posterior zygo-apophyseal joints (facet joints) may be a significant source of spinal disorders and, in many cases, debilitating pain. The articular cartilaginous surfaces can degenerate due to mechanical or biological factors and cause pain as with other joint osteoarthritis. Synovial cysts of the facet joints occur most commonly in association with degenerative disease of the spine in older individuals. The association of these cysts with trauma, rheumatoid arthritis, spondylosis and kissing spinous processes also has been reported. These cysts can cause symptoms and signs from direct compression of the dura. For example, a patient may suffer from arthritic facet joints, severe facet joint tropism or otherwise deformed facet joints, facet joint injuries, etc. There is currently a lack of suitable intervention procedures for facet joint disorders. Facet blocks with anesthetic and cortisone, facet denervation procedures, radiofrequency ablation of the nerve supply to the joint, or even spinal fusions have been recommended. In the early stages of degeneration, pain may be controlled by blocking the medial branch of the lumbar zygapophyseal (facet) joints (kryorhizotomy). However, this treatment mode of treatment is considered for temporary relief of pain. Facetectomy, or the removal of the facet joints, may provide some relief, but is also believed to significantly decrease the stiffness of the spinal column (i.e., hypermobility) in all planes of motion: flexion and extension, lateral bending, and rotation. Furthermore, problems with the facet joints can also complicate treatments associated with other portions of the spine. By way of example, contraindications for artificial joints include arthritic, deformed, unstable, or painful facet joints. Accordingly, there is a need for a facet joint treatment that addresses these concerns.
Accordingly, there is a need for effective prevention treatment of joint damage.